This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
A variety of production fluids are pumped from subterranean environments. Different types of submersible pumping systems may be disposed in production fluid deposits at subterranean locations to pump the desired fluids to the surface of the earth.
For example, in producing petroleum and other useful fluids from production wells, it is generally known to provide a submersible pumping system for raising the fluids collected in a well. Production fluids, e.g. petroleum, enter a wellbore drilled adjacent a production formation. Fluids contained in the formation collect in the wellbore and are raised by the submersible pumping system to a collection point at or above the surface of the earth.
A typical submersible pumping system comprises several components, such as a submersible electric motor that supplies energy to a submersible pump. The system further may comprise a variety of additional components, such as a connector used to connect the submersible pumping system to a deployment system. Conventional deployment systems include production tubing, cable and coiled tubing. Additionally, power is supplied to the submersible electric motor via a power cable that runs through or along the deployment system.
Often, the subterranean environment (specifically the well fluid) and fluids that are injected from the surface into the wellbore (such as acid treatments) contain corrosive compounds that may include carbon dioxide, hydrogen sulfide and brine water. These corrosive agents can be detrimental to components of the submersible pumping system, particularly to internal electric motor components, such as copper windings and bronze bearings. Moreover, irrespective of whether or not the fluid is corrosive, if the fluid enters the motor and mixes with the motor oil, the fluid can degrade the dielectric properties of the motor oil and the insulating materials of the motor components. Accordingly, it is highly desirable to keep these external fluids out of the internal motor fluid and components of the motor.
Submersible electric motors are difficult to protect from corrosive agents and external fluids because of their design requirements that allow use in the subterranean environment. A typical submersible motor is internally filled with a fluid, such as a dielectric oil, that facilitates cooling and lubrication of the motor during operation. As the motor operates, however, heat is generated, which, in turn, heats the internal motor fluid causing expansion of the oil. Conversely, the motor cools and the motor fluid contracts when the submersible pumping system is not being used.
In many applications, submersible electric motors are subject to considerable temperature variations due to the subterranean environment, injected fluids, and other internal and external factors. These temperature variations may cause undesirable fluid expansion and contraction and damage to the motor components. For example, the high temperatures common to subterranean environments may cause the motor fluid to expand excessively and cause leakage and other mechanical damage to the motor components. These high temperatures also may destroy or weaken the seals, insulating materials, and other components of the submersible pumping system. Similarly, undesirable fluid expansion and motor damage can also result from the injection of high-temperature fluids, such as steam, into the submersible pumping system.
Accordingly, this type of submersible motor benefits from a motor fluid expansion system able to accommodate the expanding and contracting motor fluid. The internal pressure of the motor must be allowed to equalize or at least substantially equalize with the surrounding pressure found within the wellbore. As a result, it becomes difficult to prevent the ingress of external fluids into the motor fluid and internal motor components.
Three primary types of motor protectors have been designed and used in isolating submersible motors while permitting expansion and contraction of the internal motor fluid. The three types of motor protectors may be utilized singularly and in combination. A first type is a labyrinth type protector that uses the differences in the specific gravity of the well fluid and the motor fluid (e.g., oil) to separate the fluids. For example, a typical labyrinth may embody a chamber having a first passageway to the motor fluid and a second passageway to an undesirable fluid, such as the fluid in the wellbore. The first and second passageways are generally oriented on opposite sides of the chamber to maintain fluid separation in a vertical orientation.
A second type is a piston type protector that moves axially in relation to the other components to adjust to a changing volume of the motor fluid. A third type is a bellows or bag type protector, wherein the bellow or bag may be formed of metal or an elastomeric material. The bellows type protectors provide two important functions: equalizing the fluid pressure within the motor and preventing well fluids (e.g., liquids and gases) from contaminating the motor fluid.
In various well applications, solids accumulate on the well fluid side of the compensating element (e.g., bellows, piston), which in time physically inhibits movement of the compensating element thereby restricting expansion of the motor oil. When the pump is turned off, the motor oil and compensator retract drawing well fluid into the protector. The well fluid, having been turbulent, can carry a high concentration of suspended solids. While the pump is inactive, the solids settle out of the well fluid around the compensation element to form a sediment bed. When the pump is started, the well fluid is expelled as the motor oil expands leaving the sediment in the motor protector. Over time this sediment bed may accumulate to a level preventing adequate movement of the compensating element. It is therefore a desire, according to one or more aspects of the present disclosure, to eliminate or to reduce the detrimental effects of solids on the operation of motor protector compensators.